Compounding the situation, rain and clouds hid signs of the toxic shower of debris, known as a pyroclastic flow, hurtling down the mountainside, hindering visual observation.

The scalding material that poured out of Fuego, which means “Fire” in Spanish, has killed 100 people, with more than 190 missing, authorities say, as rescue work on Thursday was suspended as it was too dangerous for the workers. Almost all the victims are from poor, coffee-growing hamlets on the mountain’s lower slopes that are now partially buried.